Rendering and lighting issues in blender eevee under linux
Graphics cards from the Radeon HD 6000 series are not supported, since they use the old TeraScale 2 architecture. Blender 2.8x requires GCN first generation or later when using AMD GPUs.

Supported Graphics Cards
These requirements are for basic Blender operation, rendering using the GPU requires slightly different requirements. Always make sure to install the latest drivers from the graphics card manufacturer website.

NVIDIA: GeForce 200 and newer, Quadro Tesla architecture and newer, with NVIDIA drivers (list of all GeForce and Quadro GPUs)
AMD: GCN 1st gen and newer (list of all AMD GPUs)
Intel: Haswell and newer (list of all Intel GPUs)
macOS: version 10.12 or newer with supported hardware